1. Where did you get the formula from?
2. Assuming the formula uses SI units, than the result is probably in Meter/Second not KM/Hour.
3. You can compare your results to this calculator: http://www.ebikes.ca/tools/simulator.html
4. Keep in mind that the motor produces maximum power at around 50% of it's max RPM therefore, if calculations show a 4KW power consumption at a certain speed and your motor can make only 4KW, you will have to gear the motor to spin at 50% of it's max speed when the bike is at the calculated max speed.

1. Where did you get the formula from?
2. Assuming the formula uses SI units, than the result is probably in Meter/Second not KM/Hour.
3. You can compare your results to this calculator: http://www.ebikes.ca/tools/simulator.html
4. Keep in mind that the motor produces maximum power at around 50% of it's max RPM therefore, if calculations show a 4KW power consumption at a certain speed and your motor can make only 4KW, you will have to gear the motor to spin at 50% of it's max speed when the bike is at the calculated max speed.

Avner.

1. From another german question forum.
2. Well if so, then I could go max. 28,80 kilometers per minute. And this can´t be the fact.
4. I think a brushless rear hub motor has maximum rpm when maximum power / maximum speed is used.

Be aware that maximum motor output must be geared to coincide with maximum speed.
Gearing (or winding) low will give better acceleration but never attain best speed.
Gearing (or winding) high will retard acceleration and never allow attaining best speed ... unless with tailwind, drafting or on downhill grade.

A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

DasDouble wrote:
1. From another german question forum.
2. Well if so, then I could go max. 28,80 kilometers per minute. And this can´t be the fact.
4. I think a brushless rear hub motor has maximum rpm when maximum power / maximum speed is used.

1+2 You need to check what units does the formula use, if it's in German I can't be much help.

4. That is wrong. Electric motors give maximum power at approximately half maximum RPM.

DasDouble wrote:
1. From another german question forum.
2. Well if so, then I could go max. 28,80 kilometers per minute. And this can´t be the fact.
4. I think a brushless rear hub motor has maximum rpm when maximum power / maximum speed is used.

1+2 You need to check what units does the formula use, if it's in German I can't be much help.

4. That is wrong. Electric motors give maximum power at approximately half maximum RPM.

Avner.

4. Oh ok, I see. I just thougth that you have to use as much power as you have to go to higher speed. Like at 299 km/h you have to use more powern than at 150 kp/h because of air resistance.

DasDouble wrote:
1. From another german question forum.
2. Well if so, then I could go max. 28,80 kilometers per minute. And this can´t be the fact.
4. I think a brushless rear hub motor has maximum rpm when maximum power / maximum speed is used.

1+2 You need to check what units does the formula use, if it's in German I can't be much help.

4. That is wrong. Electric motors give maximum power at approximately half maximum RPM.

Avner.

#4 Motors are capable of maximum output at ~40-50% of no load speed ... only if supplied sufficient amps!
Many motors use lighter windings and lower amps to push (reduced) maximum power to near peak efficiency and speed - 75-80%+ of no load speed

A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

Anyone here who has some datas how long it takes with a 10 kW motor from 0-100 kph / 0-60 mph?
Also I could need the weight of this rider. If so I could calculate how long you will need from 0-100 / etc. with 4 kW..

DasDouble wrote:Anyone here who has some datas how long it takes with a 10 kW motor from 0-100 kph / 0-60 mph?
Also I could need the weight of this rider. If so I could calculate how long you will need from 0-100 / etc. with 4 kW..

DasDouble wrote:
4. Oh ok, I see. I just thougth that you have to use as much power as you have to go to higher speed. Like at 299 km/h you have to use more powern than at 150 kp/h because of air resistance.

That is correct, the higher the speed the more power is needed. Theoretically, to reach twice the speed would require 4 times the power. But that does not mean the the motor is capable of supplying enough power to maintain that speed.

A motor (electric or combustion) usually delivers it peak power at a specific RPM. In order to reach the maximum speed possible, you have to gear the motor so that it is at it's peak power RPM when the vehicle is at the maximum speed.

That is why many cars can't reach their top speed in top gear. The reason is that at the theoretical top speed, in top gear the motor RPM is below the peak power RPM and the motor can't produce the power needed for that speed. At one gear lower then top, the motor RPM is higher (and closer to the peak power RPM), therefore the motor is making more power and is able to maintain a higher speed.

As has been mentioned in this thread and many others, unless it is artificially restricted, an electric motors peak power RPM is approximately half its no load RPM.

DasDouble wrote:Anyone here who has some datas how long it takes with a 10 kW motor from 0-100 kph / 0-60 mph?
Also I could need the weight of this rider. If so I could calculate how long you will need from 0-100 / etc. with 4 kW..

The velocity at any moment of time during acceleration from zero will be given by v=((2*P*t)/m)^.5 You can rearrange the equation to solve for t with v as a given, this equation neglects friction from all sources which would make the entire calculation considerably more complex.

I was answering the theoretical question, as I indicated the practical real world results will differ substantially from theoretical calculations, you add another term that would be necessary to introduce to the equation to more closely model reality.

It wouldn't be impossible to set up a controller such that a motor put out constant power over a fairly wide speed range, taper the current and hence the torque with rpm at just the right rate.

This highlights an all too common misconception, because "(or winding)" makes the otherwise correct statements incorrect. Proper gearing is critical to any electric motor application, and hubmotors are no exception, but improper gearing of DD hubmotors is the norm on ES. Winding has absolutely nothing to do with gearing. Different windings of an otherwise identical motor are capable of exactly the same torque, power, speed, acceleration, efficiency, etc. Simply vary voltage and current in the correct proportion for the same power in and power out at the same rpm and load. The only way to change the gearing of a direct drive hubmotor is to change the wheel size, and it turns out that attaining maximum speed and power from any given hubbie requires running wheels with an outside diameter smaller than 20". Due to our practical limitations on voltage, it also turns out that higher Kv DD hubmotors are capable of higher speed and power than their slow wind kiddie sisters simply because they are capable of higher rpm. That's why I typically refer to them as slower lower power motors.

You seem confused ... ?
You state that gearing and windings are totally different factors ... then you explain how windings can be enhanced-moderated by voltage and amperage >>> exactly the same methods that can be used to enhance-moderate gearing ... with the same results!.

Last edited by DrkAngel on Dec 20 2015 8:52pm, edited 1 time in total.

A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

DrkAngel wrote:You seem confused ... ?
You state that gearing and windings are are totally different factors ... then you explain how windings can be enhanced-moderated by voltage and amperage >>> exactly the same methods that can be used enhance-moderate gearing.

I have the fastest hubmotored ebike on the planet, so no I'm not confused. Voltage and current can't do anything to enhance-moderate gearing. Don't confuse yourself with vague words to try to support a misconception. Gearing is simply the mechanical relationship of the distance traveled in relation to one revolution of the motor, whether it is in the wheel or uses a chain, belt, or gears to drive wheel. If we ignore the maximum and minimum limits of voltage, different windings of the same motor are identical motors in terms of every measure of performance and capability.

DrkAngel wrote:You seem confused ... ?
You state that gearing and windings are are totally different factors ... then you explain how windings can be enhanced-moderated by voltage and amperage >>> exactly the same methods that can be used enhance-moderate gearing.

I have the fastest hubmotored ebike on the planet, so no I'm not confused. Voltage and current can't do anything to enhance-moderate gearing. Don't confuse yourself with vague words to try to support a misconception. Gearing is simply the mechanical relationship of the distance traveled in relation to one revolution of the motor, whether it is in the wheel or uses a chain, belt, or gears to drive wheel. If we ignore the maximum and minimum limits of voltage, different windings of the same motor are identical motors in terms of every measure of performance and capability.

But ... isn't the exact same thing true of different gearing of the same motor?

A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

DrkAngel wrote:You seem confused ... ?
You state that gearing and windings are are totally different factors ... then you explain how windings can be enhanced-moderated by voltage and amperage >>> exactly the same methods that can be used enhance-moderate gearing.

I have the fastest hubmotored ebike on the planet, so no I'm not confused. Voltage and current can't do anything to enhance-moderate gearing. Don't confuse yourself with vague words to try to support a misconception. Gearing is simply the mechanical relationship of the distance traveled in relation to one revolution of the motor, whether it is in the wheel or uses a chain, belt, or gears to drive wheel. If we ignore the maximum and minimum limits of voltage, different windings of the same motor are identical motors in terms of every measure of performance and capability.

But ... isn't the exact same thing true of different gearing of the same motor?

Absolutely not. Gearing multiplies or divides the torque of the motor for thrust at the wheel. Winding doesn't change anything other than the voltage and current required for the same power input and output with exactly the same efficiency and torque at a given rpm and gearing. Increase the torque/amp with more turns on the stator teeth, and the copper gets longer and thinner to exactly offset it. Current handling goes down too, so the motor is only capable of the same torque.